1. Field of the Invention
The present invention relates to a plasma processing apparatus.
2. Description of the Related Art
A plasma processing apparatus for generating plasma by applying radiofrequency power to a space between electrodes and for processing substrates by utilizing this plasma is widely known and used. In the manufacturing process of a semiconductor device, for example, a dry-etching apparatus for etching, by means of plasma, or a plasma CVD apparatus and sputtering apparatus for forming a thin film by using plasma are commonly utilized.
In these conventional plasma processing apparatus, for example in a dry-etching device, parallel plain electrodes consisting of upper and lower electrodes are provided in a chamber, and a semiconductor wafer having a thin film formed on its surface is placed on the lower electrode. The thin film on the surface of the semiconductor wafer is dry-etched the thin film by introducing a process gas into this chamber and supplying a predetermined radiofrequency power to the space between the upper and lower electrodes to generate plasma. Generally, in order to cool a semiconductor wafer which is being processed, a cooling mechanism for circulating a refrigerant in the lower electrode is provided in the apparatus.
In a current dry-etching apparatus, however, a refrigerant at a low temperature of almost -30.degree. C. is circulated to cool a semiconductor wafer, and there occurs the problem that condensation occurs at a portion cooled by a cooling mechanism, for example, a refrigerant circulating pipe or a metal cover for covering cooled portions. This tendency is particularly pronounced in the case of cooling a wafer by using liquid nitrogen. In order to resolve this problem, selection of a resin having a low thermal conductivity for use as the material of the cover has been attempted. However, if a resin is used as the material for forming the cover, there occurs a problem in that leakage of radiofrequency occurs.
Therefore, a plasma processing apparatus having a cooling mechanism which can prevent the occurrence of condensation and at the same time prevent radiofrequency leakage is yet to be sufficiently realized.